Acute respiratory distress syndrome (ARDS) remains a major clinical problem in both adult and pediatric intensive care medicine. It carries high morbidity and mortality rates, and no current therapies are directed at the underlying molecular mechanisms of disease. As recent experience with novel respiratory infections (e.g., SARS, H1N1) has demonstrated, ARDS also has the potential to become a major public health crisis. Key features of ARDS are increased permeability of the alveolar-capillary barrier, oxidant production with disrupted redox signaling, and intense lung inflammation. Epigenetic mechanisms, including microRNAs (miRNA), regulate important changes in gene expression in cardiovascular diseases, respiratory diseases, and cancer. The contribution of miRNAs to the pathophysiology of ARDS, however, remains obscure. We hypothesize that: (1) changes in miRNA expression contribute to ARDS; (2) among those changes, loss of miR-26a derepresses EphA2 while increases in miR-21 blunt SOD3 expression, resulting in increased permeability, oxidant damage and inflammation; (3) EphA2-targeted nanoparticle-based delivery of miRNA therapeutics may be a viable means of modulating the disease process. We present a strong rationale and compelling preliminary data to focus our study on these two miRNA/gene target pairs: miR- 26a/EphA2 and miR-21/SOD3 in animal models of ARDS and critically ill pediatric patients with ARDS. We have generated nanoparticles coated with the YSA peptide that selectively binds to EphA2, enabling us to deliver miRNA modulators to the endothelium where EphA2 is expressed via these YSA-nanoparticles. We propose three Specific Aims. Aim 1: Test whether ARDS causes a change in key miRNAs (miR-26a and miR-21) that regulate key gene targets (EphA2 and SOD3) important in increased vascular permeability and insufficient antioxidant defenses. Using direct (intratracheal bleomycin) and indirect (intraperitoneal LPS) mouse models of ARDS, we will determine if ARDS alters miR-26a and miR-21 expression in lung. We will test the impact of altered miRNA expression on key gene targets in relevant cell culture models, determining whether loss of miR-26a contributes to increases in EphA2, and whether increased miR-21 suppresses expression of SOD3. We will also measure plasma miRNA expression changes in a cohort of critically ill children with ARDS to provide a clinical correlate to the animal models. Aim 2: Test whether functionalized nanoparticles targeted to bind EphA2 can improve delivery of nanoparticles to the injured lung. We will use cell culture models as well as whole animal studies including intravital microscopy to study the delivery, distribution, and fate of YSA-nanoparticles in normal and injured lung, determine the effects of those nanoparticles on lung permeability and inflammation, and establish the ability to use these nanoparticles to selectively deliver miRNA to the injured lung. Aim 3: Test whether functionalized nanoparticle delivery of miRNA mimics can ameliorate increased permeability, oxidant stress, and inflammation in the injured lung. In the final aim, we will use the YSA-nanoparticles to deliver miR-26a mimics and miR-21 antagonists to the injured lung and determine if they change the expression of EphA2 and SOD3 and mitigate against increased vascular permeability, oxidative stress and inflammation.